Pneumatic Nail Gun: Main Valve, Return Chamber and Fast Trigger Valve

Hitachi Koki's air nailer (US 7,156,012, 2007). Compressed air stored in the handle holds a main valve shut over the cylinder. Pulling the trigger with the nose pressed to the work vents a small trigger-valve chamber, which vents the main-valve chamber; the main valve jumps up, closes the exhaust and lets stored air throw the piston and driver blade down onto a nail. Air caught below the piston in a return chamber pushes it back up. Hitachi sized the valve chambers against their vents to make the gun fire and reset faster. The patent gives no materials, bore, stroke, air pressure or nail size. The picture: the patent's Fig. 1.